In the field of cardiac pacing and/or defibrillation, therapy delivery from an implanted medical device may rely upon cardiac signals sensed and pacing therapy delivered via a bipolar pair of implanted electrodes included on one or more medical electrical leads coupled to the medical device.
With respect to sensing, accurate detection and classification of arrhythmias relies upon an adequate signal-to-noise ratio picked up by the bipolar pair of electrodes; the signal being a near-field cardiac conduction signal and the noise being either a far-field cardiac conduction signal or electrical activity in other muscles of the body or a combination thereof. Many medical devices incorporate sensing algorithms to blank or ignore far-field signals, however this may lead to under-sensing or under-detection of fast regular rhythms. As an alternative, a spacing between the bipolar pair of electrodes on the lead may be decreased in order reduce and localize the field of sensing between the two electrodes.
With respect to pacing, an effective stimulating pulse is focused via intimate tissue contact with a first electrode, serving as a cathode, included in the bipolar pair; if a second electrode of the bipolar pair, serving as an anode, comes too close to active tissue there is a chance of anodal stimulation, which impairs the therapy delivery.